Carbon-pile rheostat of the foot operated type



Feb. 11, 1969 s. TANZMAN 3,427,545

CARBON-FILE RHEOSTAT OF THE FOOT OPERATED TYPE Filed Nov. e, 1967 Sheet of INVENTOR Feb. 11, 1969 s. TANZMAN 3,427,545 v CARBON-FILE RHEOSTAT OF THE FOOT OPERATED TYPE ila'i Jov. 1967 Sheet 3 of z? I r I I Z M. @l HI. 2

7 15 INVENTOR j! 35 03401061. FINE 77AM United States Patent 6 Claims ABSTRACT OF THE DISCLOSURE A foot-operated rheostat of the carbon-pile type having a carbon-pile resistance element mounted in a ceramic block with one end of the resistance element being exposed for the making of electrical contact therewith and the application of pressure thereon and in which members for contacting and exerting pressure on said exposed end of the resistance element are pivotally mounted at their ends between a terminal strip and a portion of a ceramic block. One of said members being of an electrically conductive material such as brass and the other of said members being of a resilient material such as spring steel with the electrically conductive member being interposed between the exposed end of the carbon-pile resistance element and being moved into and out of engagement therewith in response to angular movement of the other of said members.

The present invention relates to a rheostat and it relates, more particularly, to a foot-operated rheostat of the carbon-pile type for use in controlling the operation of electrical motors for sewing machines and similar appliances.

An object of the present invention is to provide a footoperated rheostat of the carbon pile type which is simple and economical to manufacture and which will provide an effective speed control from an off position to a substantially full speed position.

In a rheostat embodying the present invention, bending stresses exerted on the movable members which. contact with and exert pressure on the resistance element, are minimized and the risk that such members will break due to metal fatigue under repeated bending stress is reduced.

These and other objects and advantages of the invention will be better understood from the following description and the accompanying drawings, in which:

FIG. 1 is a perspective view of a foot-operated rheostat embodying the invention;

FIG. 2 is a perspective view illustrating certain parts of the rheostat shown in FIG. 1, but with the housing and foot pedal removed;

FIG. 3 is a bottom plan view of the parts of the rheostat shown in FIG. 2, but is drawn to an enlarged scale;

FIGS. 3A and 3B are fragmentary views of a portion of the parts shown in FIG. 3 but with operating members in different positions;

FIG. 4 is a section view taken along the line 4-4 of FIG. 3;

FIG. 5 is a section view taken along the line 5-5 of FIG. 1 but is drawn to an enlarged scale;

FIG. 6 is a plan view of one of the operating members for the rheostat shown in FIG. 2;

FIG. 7 is a fragmentary view in partial section illustrating a connection between an operating link and a control member forming part of the rheostat shown in FIG. 1; and

FIGS. 8, 9 and 10 are, respectively, a plan view, a side elevational view and an end view of a second control member for the rheostat shown in FIG. 2.

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Referring to the drawings in detail, FIG. 1 illustrates a foot-operated rheostat 10 of the carbon-pile type which includes a metal housing 11 which can be placed on the floor or other convenient position.

A foot pedal 12 is pivotally supported on the top of the housing by a shaft 13 which extends across the housing and is supported at its ends in ears 14 which are struck up from the top of the housing.

As shown best in FIG. 5, the forward or free end of the foot pedal is biased upwardly or toward a raised position by means of a coil spring 15 which surrounds the pedal supporting shaft with its ends 15a and 15b engaging, respectively, with the top of the housing and the lower surface of the forward end of the foot pedal. The foot pedal carries an operating arm 16 which extends downwardly through an opening in the top of the housing at the rear of one of the shaft-supporting ears. Thus, when the forward end of the foot pedal is depressed against the force of the coil spring, the operating arm is swung rearwardly as indicated by the dot and dash lines in FIG. 5. In the raised position of the pedal, the rear end thereof engages with the top of the housing and acts as a stop.

The end of the operating arm is pivotally connected to one end of a link 17 of insulating material which extends forwardly and is connected at its other end to a movable end of a control or operating member 18 of a resilient material such as spring steel which is pivotally mounted at one end of a resistance unit 19 located inside of the housing. As shown in FIGS. 2 and 7, the end of the connecting link extends through a slotted opening 20 in the control member and portions of the control member extending along opposite sides of the opening therein fit into slots 21 in the link so as to provide a loose connection between these parts. In addition, the control member has trunnions 22 extending from opposite sides thereof adjacent its other end for pivotal mounting of the control member as will be described.

The resistance unit comprises a block 23 of ceramic insulating material having a cylindrical chamber 23a formed therein in which disc-like carbon elements of a carbon-pile resistance 24 are mounted. A terminal 25 of an electrically conductive material is attached to the ceramic block at one end thereof and has a plate-like portion 25a which extends over the end of ceramic block opposite an opening at one end of the resistance chamber to support and make contact with one end of the resistance element located therein. A portion 26 of the terminal is provided with the usual connecting screw for connecting one side of an electric line to the terminal and thus, to one end of the resistance element.

The other end of the carbon-pile resistance element carries a cap 27 of electrically conductive material which projects through an opening at the other end of the resistance chamber. A second terminal 28 in the form of an elongated strip of electrically conductive material is attached to and extends lengthwise of the ceramic block and has an end 29 with a connecting screw extending beyond one end of the ceramic block for connection of the other side of the electrical line thereto.

The other end 30 of the terminal strip extends beyond the other end of the block and contains an opening 31 which is aligned with and in spaced relation to an opening or recess 32 in an ear-like projection 33 which extends outwardly from the end of the ceramic block. One of the trunnions adjacent the end of the spring steel control member is journalled in the opening in the terminal strip and the other trunnion is journalled in the recess in the ear-like projection. Thus, the spring steel control member is pivoted at one end and it extends across the end of the ceramic block in opposing relation to the end cap on the resistance element.

In addition to the spring steel member, there is a second control member 34 of brass or other electrically conductive material having trunnions 35 which extend from opposite sides adjacent one end thereof. The trunnions of the second control member are also. journalled in the opening in the terminal strip and in the recess in ear-like projection with an electrical connection being made between the conductive control member and the terminal strip.

The other or free end of the second control member is interposed between the spring steel control member and the end cap of the resistance so as to make electrical contact with said cap in operation of the rheostat. The free end of the second control member is bent so that it slopes slightly away from the spring steel strip and toward the cap on the resistance element. The outer end of the second control member is bent so as to extend through the slotted opening in the spring steel control member with a headed portion 36 being located on the outer side of the spring steel member. This provides a loose connection which permits a limited angular movement between the control members in operation of the device. For example, the control members move together until the member of conductive material has been brought into contact with the end cap of the resistance element as shown in FIG. 3A. This establishes electrical contact between the resistance element and the conductive member and as movement of the spring steel member is continued, it engages with the conductive member as shown in FIG. 3B and pressure is exerted on the carbon-pile resistance element causing the resistance thereof to be decreased. With this arrangement, the pressure exerted on the carbon-pile resistance element by means of the pivoted spring steel member can be increased to a point where the resistance of the resistance element becomes negligible and hence, it is not necessary to provide shunting contacts which bypass the resistance element in order to obtain full power.

It will also be noted that the pivotal mounting of the two control members between the end of the terminal strip and the ear-like projection on the ceramic block minimizes bending stresses to which the control members are subjected and thus, reduces the risk of their breaking due to metal fatigue.

When pressure is released from the foot pedal, the coil spring associated therewith returns the foot pedal to its raised position as shown in FIG. 1 and this automatically returns the control members to the positions shown in full lines in FIG. 3 where the connection between the cap on the resistance and the second control member is interrupted.

It will be understood that various changes and modifications may be made in the embodiment of the invention illustrated and described herein without departing from the scope of the following claims.

1. In a rheostat of the carbon-pile type, the combination which comprises:

(a) a body of insulating material having a chamber formed therein;

(b) said chamber having openings at opposite ends of said body;

(c) a carbon-pile resistance element located in said chamber;

(d) said resistance element having an end extendirfg through one of said openings and being exposed at the end of said body for the application of pressure thereto;

(e) a terminal member of electrically conductive ma terial carried by said body of insulating material and having an end extending outwardly from said one end of said body;

(f) a projection formed on and extending outwardly from said body at said one end thereof in opposing and spaced relation relative to the outwardly extending end of the terminal member; and

(g) a contact arm of electrically conductive material pivotally mounted on said body;

(h) one end of said contact arm being connected to the outwardly extending end of the terminal member and being pivoted between said outwardly extending end of the terminal member and the projection on the body of insulating material;

(i) said contact arm extending in opposing relation to the exposed end of the resistance element and belng pivotally movable into and out of contacting engagement and pressure-applying engagement therewith.

2. In a rheostat of the carbon-pile type, the combination as defined in claim 1 wherein:

(a) the body of insulating material comprises a block of ceramic material.

3. In a rheostat of the carbon-pile type, the combination as defined in claim 1 which includes:

(a) a second terminal member of electrically conductive material carried by the body of insulating material;

(b) said second terminal member including a portion extending over the other of said openings to the chamber in said body;

(c) said terminal portion being in electrical contact with the resistance element at an end opposite the exposed end thereof and supporting the resistance element against lengthwise movement relative to the body of insulating material.

4. In a rheostat of the carbon-pile type, the combination as defined in claim 3 which includes:

(a) a movable member of resilient material positioned to engage with and move the contact arm into engagement with the exposed end of the resistance element;

(b) said member having an end pivoted between the outwardly extending end of the terminal member and the projection on the body of insulating material at a point common with the pivoted end of the contact arm.

5. In a rheostat of the carbon-pile type, the combination which comprises:

(a) a block of ceramic material having a chamber formed therein;

(b) said chamber having openings at opposite ends of the ceramic block;

(0) a carbon-pile resistance element located in said chamber;

(d) said resistance element having an end extending through one of the openings in the ceramic block; (e) said end of the resistance element being exposed for establishing an electrical connection thereto and for application of pressure to the resistance element;

(f) a terminal member carried by said ceramic block;

(g) said terminal member comprising a strip of electrically conductive material having an end extending beyond the ceramic block at a point spaced from the exposed end of the resistance element;

(h) a projection formed on the ceramic block and extending therefrom in opposing relation to said end of the terminal member;

(i) a movable contact arm of flexible material extending across the ceramic block at said one end thereof in opposing the exposed end of the resistance element; I

(j) said contact arm being pivotally mounted at one end thereof between said projection and the outwardly extending end of the terminal member and being electrically connect-ed at said end to the terminal member; and

(k) means for pivotally moving said contact arm into engagement with the exposed end of the resistance element and applying pressure thereto;

(1) said means including a strip of resilient material;

(in) said resilient strip being pivoted at one end between the end of the end of the terminal member and the projection on the ceramic block at a point commen with the end of the contact arm and being positioned on a side of the contact arm facing away from the exposed end of the resistance element.

6. In a rheostat of the carbon-pile type, the combination as defined in claim 5 wherein:

(a) the strip of resilient material includes a portion spaced from the contact arm Where said arm opposes the exposed end of the resistance element;

(b) said portion of the resilient strip being resiliently movable into engagement with the contact arm upon engagement of the contact arm with the exposed end of the resistance element.

References Cited UNITED STATES PATENTS Chason 338108 Naul 338-108 Schenk 338108 Bell 338--108 Anderson 338-408 X Voorlas 338-108 10 ROBERT K. SCHAFER, Primary Examiner.

H. I HOHAUSER, Assistant Examiner. 

